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AV-SCANNER / Service function guides / Fuel and emissions
This guide covers the complete diagnostic and service procedure for nitrogen oxide (NOx) sensors on modern diesel engines, from understanding the system's operation to performing replacement and verifying the repair. It is written for working mechanics and experienced DIYers who already have a solid grasp of diesel aftertreatment systems and scan tool diagnostics. After reading, you will be able to systematically test NOx sensors, interpret live data and fault codes, replace sensors correctly, and confirm the fix with road tests and scan tool data. The guide also prepares you for model-specific variations and common pitfalls that can turn a simple sensor swap into a comeback.
Guidance is general and covers many makes. Exact procedures and values vary by model, so confirm them in the factory service information for your vehicle.
Download all 12 sections as a branded PDF to use in the workshop.
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